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This article in AJ

  1. Vol. 77 No. 5, p. 743-752
    Received: Oct 1, 1984

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Estimation of Spring Wheat Grain Dry Matter Assimilation from Air Temperature1

  1. Armand Bauer,
  2. A. B. Frank and
  3. A. L. Black2



Modelers and forecasters of crop growth and yield would benefit from a meterologically based index that precisely describes postanthesis development of spring wheat (Triticum aestivum L.). Five field trials over a 3-yr period were conducted on Williams loam (fineloamy typic Argiboroll) in which grain dry matter assimilation was measured in hard red spring wheat cultivars grown under different management practices. The measured parameters were regressed on cumulative growing degreedays (GDD), base temperature 0 °C, and days (DAYS) after anthesis. Over the grain yield range 1488 to 3876 kg ha−1, both GDD and DAYS accounted for 93% of the variability in grain dry matter assimilation among all trials. Maximum average kernel number of 21.8 spike−1 was attained when 250 GDD had been accumulated or 12 DAYS after anthesis, and maximum average kernel mass of 27.1 mg after about 770 GDD or 35 DAYS. Constantrate assimilation, from 175 to 630 GDD, was 0.049 mg GDD−1 kernel−1, and between 9 and 26 DAYS it was 1.08 mg DAY−1 kernel−1. With an average of 447 spikes m−2 and average kernel number and mass, constant-rate phase assimilation was 4.77 kg GDD−1 ha−1 or 104 kg DAY−1 ha−1. Among the variable water and N regimes and cultivars, largest differences in assimilation resulted from soil water supply during heading. With < 65 mm available water, constantrate phase assimilation was as low as 0.038 mg GDD−1 kernel−1 and with > 84 mm as high as 0.066 mg GDD−1 kernel−1. The greater constant-rate assimilation was accompanied by a shorter grain-filling duration. Filling duration was shorter when available N levels exceeded the amount needed for the highest grain yields than with N levels which increased yields. Cultivar differences in harvest kernel weight resulted from differences in lag phase assimilation rate.

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